Getting new products to the market faster than one's competition is recognized as a key to gaining a large market share. Thus, there is an incentive to speed up every step of new product development. One area of product development having a significant impact on overall market timing is the making of product and package prototypes for market testing. Such testing usually requires multiple look-like, feel-like, and function-like prototypes for consumers to examine or use.
Where production quantities are needed, molding is the normal way of producing parts. Production molding typically involves plastic parts made in very expensive, multiple cavity, steel molds. For example, most bottles are blow-molded and most bottle closures are injection molded. It usually takes large production quantities to justify the cost of a production mold. For market testing, on the other hand, only a few hundred parts may be needed. However, it is often necessary to mold prototype parts so that they have the same characteristics as production parts.
How to rapidly obtain molded prototype parts is therefore the challenge. Some solutions already exist for rapidly making prototype part molds from which a small quantity of parts can be cast. For example, refractory powders and a thermoplastic binder can be combined under heat in a flexible rubber pattern. This process forms a green article, which is then heated further to melt out the binder. Infiltrating the resulting porous article with a molten, low melting point metal forms a mold of high density which is free of machined surfaces. The disadvantage of this process is that the powders are sintered in order to hold the mold together after the binder is removed. Sintering causes particles to occupy less space than they would occupy unsintered. Thus, sintering shrinkage influences the accuracy of the mold and the parts made therefrom.
A sintered metal article having channels, such as for cooling fluid, may be formed by combining copper wires with sintering powders. Upon application of the sintering temperature, the wires melt and are absorbed into the pores of the sintered particles to form channels.
Another method for rapidly prototyping pans is investment casting, using patterns generated by rapid prototyping systems instead of traditional injection molded wax patterns. An example of such a pattern is a QuickCast.TM. pattern, which is a trademark of 3D Systems, Inc. of Valencia, Calif. A hollow plastic pattern is coated with a thin ceramic shell, usually by a dipping process. The plastic is burned out of the ceramic shell leaving minimal amounts of ash residue behind. Molten metal is then poured into the ceramic shell to cast a metal part or a metal mold for a plastic part. Because the shell has only a small hole for admitting molten metal, it is difficult to inspect the critical surfaces for ash residue. Any ash remaining on a critical surface will potentially ruin the metal casting. The molten metal cools and shrinks such that critical surfaces are not reproduced accurately. The larger the parts, the greater the inaccuracy.
Improvements to the investment casting process utilize a ceramic shell which is created around a pattern by pouring a ceramic slurry and a binder that is chemically controlled to provide for precise setting of the ceramic shell. This is an improvement to the investment casting process because shell-making is faster. However, investment casting is still limited to small size molds where molten metal shrinkage does not exaggerate inaccuracies.
What has been missing is a method for rapidly making accurate metal mold halves primarily for injection molding purposes, independent of part size, which enables a relatively large number of plastic pans to be molded therefrom.